The present invention relates to the measurement of the overall deformation of a tire particularly during use i.e. while the respective vehicle of which the tire is a part is being driven. The invention also relates to the measurement of the overall deformation of a tire in such a manner that distance changes that occur in a cross-sectional plane and relative to a representative reference point whereby the reference point and a measuring point are located inside the tire, and distance changes are specifically ascertained through an appropriate transducer. In addition the invention relates to a series arrangement of a force measuring transducer and of an elastic member in general.
The stiffness of a tire i.e. its vertical and lateral resilient reaction are important factors particularly for passenger comfort and vehicle handling but also for the life of the tire. For optimizing the design of a tire its vertical and its lateral deformation during use has to be ascertained in appropriate test runs and even at high speeds.
H. C. A. van Eldik of the U.S. Department of Transportation has published a textbook "Mechanics of pneumatic tires" under DOT H5 805952 of August, 1981 and page 577 refers to a method of measurement as alluded to in the introductory paragraph. Herein a flexible cable or rope is used and put under tension by a spring while one end is connected to the center of the inside surface of the tire, opposite the running surface while its other end is connected a potentiometer mounted in turn on the rim. In the case of a vertical deformation the cable adjusts the potentiometer and the commensurate modification of the tapped resistance serves as measuring value for the deformation of the tire. This approach is disadvantaged by the fact that the potentiometer will respond to also lateral deformations even though there are no vertical deformations or in the case of a combination deformation the vertical and lateral components of the tire deformation can really not be separated to the requisite degree.
German printed patent application No. 33 01 173 describes a device for acquiring the belt positions in a pneumatic tire wherein the belt itself is capable of detuning an electric oscillating circuit (11 in the reference) which in turn controls an indicator. In particular, the oscillating circuit is varied in dependence upon the angular (azimuthal) inclination of the steel cable of the belt cable 8 in that reference. This way then permits ascertaining of the correct position of the steel wires 8 of the belt particularly during tire manufacturing. Thus this publication refers to quality control of the manufacturing process. Such a control is, of course, necessary since one wants to check whether the belt layers are properly positoned, bearing in mind that often manual labor is involved in the making of such a tire. It is clearly a disadvantage if these belt layers and cable laterally shift during the manufacture.
German printed patent application No. 31 37 248 (based on U.S. patent application Ser. No. 188,707 of Sept. 19, 1980) discloses a method for predicting variables in a tire whereby a tire is rotated relative to a first measuring equipment and any lateral deflection on one side of the tire is measured in a position between the area of maximum cross-section (SD) and the outer radial surface. The tire is also rotated relative to a second measuring device to ascertain lateral deflection of the other side of the tire and with reference to a second position which basically has the same radius as the first mentioned position. In order to acquire the tire variable of interest one ascertains the first harmonics for the deflections in each of the peripheral positions and adds them up for different peripheral positions around the tire. This method basically provides for a scanning of any lateral deflection of the tire so that only certain areas of the outer tire wall are in fact monitored, but not the running surfaces of the tire nor internal deformations. Moreover the two measuring equipments used in that method are stationary as the tire rotates so that no measurement occurs as between the tire on one hand and the rim of the wheel on the other hand.
Independent from the foregoing and unrelated to the measurement of tire deformations, equipment is known in which force per se is measured in conjunction with a positioning spring. For example, German printed patent application Nos. 33 09 524 and 10 68 911 as well as German Pat. No. 958,511 describe measuring transducers in which a series arrangement is provided between a force measuring element and an elastic member. In all of these cases one uses the force measurement for ascertaining a compression or a tension force as such.